1. Field of the Invention
The present invention relates to a zoom finder device, for changing a finder magnification in cooperation with zooming of a taking lens.
2. Background Arts
A zoom compact camera adopts a zoom finder device, using a zoom lens as a taking lens. The zoom finder device varies finder magnification in cooperation with a zooming of the taking lens. In a recent zoom compact camera, it is widely used a zoom finder device of real image system that contains a finder optical system in compact. According to the zoom finder device of real image system, a subject image is focused on an image plane in the finder optical system as an aerial image, which is magnified to observe through an eyepiece lens. For instance, as disclosed in Japanese Patent Laid-open Publication No. 9-211556, the finder magnification is changed by use of a cam, which moves in cooperation with zooming of the taking lens, to move the finder zoom lens disposed in front of the imaging plane.
It is necessary to adjust the focus of an eyepiece lens on the image plane of aerial image to facilitate a finder image to observe. If proper adjustment is not performed, it is extremely hard to observe the aerial image depending on a photographer""s vision. Standard visibility adjustment is performed upon manufacture. For adjustment visibility, the eyepiece lens is moved to an optical axis direction, to coincide the focus of the eyepiece lens with the aerial image plane.
As disclosed in Japanese Patent Laid-open Publication No. 11-231199, many recent compact cameras use a step zoom system that sets a zooming position of the taking lens stepwise. The step zoom system puts a focusing section between two zooming sections, to conduct zooming and focusing alternately while a movable lens barrel is rotating successively. The step zoom system can perform zooming and focusing by a single lens motor. Furthermore, there is a way for keeping the taking zoom lens in contact with one side of a cam groove so as to position the taking zoom lens in a right position, without an influence of backlash of gear and cam. On setting the movable lens barrel at a desired zooming position, it stops the movable lens barrel while moving from a predetermined direction at any time, regardless of either zooming towards a telephoto end or a wide-angle end. In other words, according to the camera that the lens motor makes a forwarding rotation to zoom from the wide-angle end to the telephoto end to stop, on zooming from the telephoto end to the wide-angle end, the lens motor makes a reverse rotation to move the movable lens barrel a little over the predetermined zooming position, then rotates the lens motor forward for the surplus to stop the movable lens barrel at the predetermined zooming position.
As a surplus space is more and more scarce around the eyepiece lens with the progress of compact of a camera, visibility adjustment by moving the eyepiece lens is becoming hard. For instance, in case the eyepiece lens and an erect prism are integrally formed by plastic so as to compact the zoom finder device, the erect prism must be moved for visibility adjustment. This not only prevents the zoom finder device from realizing compactness, but also complicates structure.
Since the finder magnification is changed in accordance with the drive of the lens motor, the step zoom system also moves the finder lens in spite of the drive of the lens motor for focusing. It is not preferable for causing a change of finder magnification. Furthermore, on keeping the taking zoom lens in contact with one side of the cam, it causes a change of finder magnification during the offset. And making use of the offset stroke for focusing of the taking lens also changes the finder magnification.
A main object of the present invention is to provide a zoom finder device that can adjust visibility without making a finder optical system complicated.
Another object of the present invention is to provide a zoom finder device, for adjustment visibility with an eyepiece lens fixed.
Further object of the present invention is to provide a zoom finder device whose finder magnification is unchanged while focusing a taking lens or offsetting a taking zoom lens.
To attain the above objects and the other objects, according to the zoom finder device of the present invention, a cam cylinder which changes finder magnification is slidable in an axial direction. By adjusting the position of the cam cylinder in the axial direction, the visibility adjustment of the finder optical system is conducted. A driving gear makes a rotation in cooperation with zooming of the taking lens. The rotation of the driving gear is transmitted to the cam cylinder through a transmission mechanism, and in cooperation with zooming of the taking lens the finder magnification is changed. The transmission mechanism has an idle section that the driving gear gets disconnected with the cam cylinder. When the driving gear is switched its rotational direction for focusing or keep one-sided, the finder magnification is unchanged on account of the idle section.
According to the preferred embodiment of the present invention, it is provided with a compression coiled spring and an adjustment screw. The compression coiled spring is stored in a hollow part of the cam cylinder, for urging the cam cylinder in a direction to separate from the driving gear. And the adjustment screw, which is threaded into the finder frame to support the cam cylinder rotatably, receives the edge of the cam cylinder whose tip is biased by the compression coiled spring. The position of the cam cylinder in the optical axis direction is adjusted by the insertion amount of the adjustment screw. Furthermore, a cutout and a projection are formed in the cam cylinder and the driving gear. The region where the projection moves within the cutout becomes the idle section.
According to the present invention, visibility of the finder optical system can be adjusted without making the finder optical system complicated and with the eyepiece lens fixed, by moving the cam cylinder in an axial direction. Visibility of the finder optical system is easily adjusted by changing the insertion amount of the adjustment screw. In addition to that, since the idle section is formed in the transmission mechanism that transmits zooming movement to the cam cylinder, the finder magnification is not changed during focusing or the offset of the step zoom.